The invention relates to a magnetic resonance method for forming a fast dynamic image form a plurality of signals of an RF probe The invention further relates to a magnetic resonance imaging apparatus for obtaining a fast dynamic image and to a computer program product.
It is common practice to perform MR image acquisitions in which the patient position is physically moved through the magnet bore between a group of successive scans. At the end of this multi-station scanning, the resultant images are combined to a single large image. This approach is known e.g. from WO-A-02/04971, which allows to image a much larger FOV than the limits of the magnet homogeneity, gradient linearity and RF coil uniformity normally allow. In this document a MR imaging method is described which involves the acquisition of sets of MR signals form several scan-volumes of an object. Different spatial approaches are taken in the scanning of the respective scan-volumes. In particular respective scan-volumes include different numbers of scan-slices or scan slices of respective scan-volumes have a different slice thickness or scan-slices of respective scan-volumes have different FOV's (Fields Of View).
In U.S. Pat. No. 5,636,636 a magnetic resonance method and device is described in which an object to be examined is displaced at a defined speed relative to an examination zone and a plurality of sequences act on the examination zone in the presence of a steady, uniform magnetic filed. Each of the sequences includes at least one RF pulse and possibly a phase encoding gradient. An MR signal arising in the examination zone, after transposition to another frequency range by means of an oscillator signal, is used to produce an MR image. The method aims to enhance the quality of the MR image by preventing movement artefacts. This is achieved in that from one sequence to another, one or more of the frequency of the RF pulses, the frequency of the oscillator signal and the phase position of the oscillator signal is adjusted in conformity with the position of the object to be examined relative to the examination zone so that a part of the object which is imaged in the MR image moves relative to the examination zone in synchronism with the object.
In EP-A-1 024 371 a magnetic resonance imaging apparatus is described in which excitation pulses are applied to a restricted region of the bore of the MR imaging magnet in which the magnetic field is uniform. The data samples collected are Fourier transformed to form a volumetric image of the restricted region. A motor continuously moves a patient couch so that a region of interest passes through the region of the good field. The collected data samples are corrected to compensate for the motion so that a volumetric image is formed of greater length than that of the restricted region.
Since all the above-mentioned methods require a full scan within the restricted FOV imaging of the full object will take quite a long sampling time It is an object of the present invention to provide a method for forming an MR image from data sampled in an array of adjacent FOV's in shorter time. It is a further object of the invention to provide an adequate apparatus and a computer program product for exercising the method.
It is a main advantage of the present invention that images with suitable large FOV's are obtained with a short magnet in shorter time.
These and further advantages of the invention are disclosed in the dependent claims and in the following description in which an exemplified embodiment of the invention is described with respect to the accompanying drawings. It shows